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Grazing incidence X-Ray scattering from the interfaces of thin film magnetic device materials

Abstract

Thin film devices have found many applications in recently developed technology. With the need to increase data storage capacity and performance there are ever more demanding requirements of these devices. Gaining an understanding at the atomic scale of the growth and subsequent manufacturing treatments is fundamental to improving the device design. Grazing incidence x-ray scattering techniques have been used to study the interfaces in a sequence of samples, starting with repeated bi layers of single element material and sequentially working up to a realistic Magnetic Tunnnel junction (MTJ) structure. The width of the diffuse Bragg sheet from repeated bi-layers of Co/Pd and Co/Ru shows that the correlation length of the out-of-plane toughness is shorter for higher frequency roughness components than longer wavelength features. Scaling behaviour in the intensity profile demonstrates that the interfaces become more two-dimensional as more layers are deposited Reflectivity measurements with in-situ annealing reveal that the interfaces in CoFe/Ru repeated bi-layers are stable with temperature. The interfaces of amorphous CoFeB with ruthenium are also stable until the CoFeB crystallises. Similar measurements on repeated bi-layers of CoFeB/AlO, show sharpening of the interface during annealing. The diffuse scatter shows this to be a reduction in the intetdiffusion of the interface and not a change in topological roughness. The scatter from a single CoFeB/A10, interface on a realistic MTJ sub-structure also shows changes with annealing which are consistent with interface sharpening. This sharpening is matched to enhancements in the tunnel magneto- resistance of the MTJ. The changes occurring cannot be explained solely by sharpening of this particular interface and more sophisticated modelling has been attempted to identify the changes. Simulations show that changes in the manganese profile from an IrMn pinning layer in the MTJ should result in a significant change in the variable energy reflectivity recorded at a constant scattering vector.